Crankshaft and marine engine

Abstract

The present invention discloses a crankshaft and a marine engine. The crankshaft is formed by combining a crankshaft journal and a crank arm by shrink fitting. The crank arm has a circular opening for inserting the crankshaft journal. If the crank arm is observed along the central axis of the opening, the direction connecting the central axis of the crank pin and the central axis of the opening is set as the first direction, the direction orthogonal to the first direction is set as the second direction, and the difference between the dimension from the central axis of the opening to the outer surface of the crank arm and the inner radius (R) of the opening is taken as the thickness around the opening. The thickness around the opening in the second direction (T2) will be greater than the thickness (T1) of the part on the opposite side of the crank pin sandwiching the opening in the first direction. Good torque transmission is achieved and damage to the main bearing is suppressed without causing enlargement of the internal combustion engine chamber.

Description

Technical Field

[0001] The present disclosure relates to a crankshaft and a marine engine including the crankshaft. Background Art

[0002] A crankshaft in which at least the crank arm and the crank journal among a crank pin, a crank arm and a crank journal are combined by shrinkage fit is a well-known crankshaft.

[0003] For example, a so-called semi-assembled crankshaft is disclosed in Patent Document 1. The crankshaft includes a web formed by integrating a crank pin and a crank arm, and a crank journal (a main shaft supported by the journal: journal shaft) shrunk onto the web.

[0004] Another example of a semi-assembled crankshaft is disclosed in Non-Patent Document 1. Specifically, Non-Patent Document 1 discloses a technical content that the outer surface of the crank arm near the opening for inserting the crankshaft journal is formed into an arc shape, and the outer surface and the opening are arranged coaxially.

[0005] According to the above-mentioned Non-Patent Document 1, the thickness in the radial direction around the above-mentioned opening is kept substantially constant.

[0006] Patent Document 1: Japanese Utility Model Publication No. 52-151218

[0007] Non-patent document 1: Masuichi Yasuda, Isao Sakamoto, and Suehiko Tsuji, "Repeated Bending Fatigue Strength of Semi-Composite Crankshafts", Proceedings of the Shipbuilding Association, No. 112, 1962 Summary of the invention

[0008] -Technical problem to be solved by the invention-

[0009] In order not to hinder the torque transmission, the surface pressure of the shrink fit portion of the crankshaft as described above is required to be kept high. Therefore, for example, it is conceivable to design the shrink fit margin between the opening of the crank arm and the crankshaft journal as large as possible.

[0010] However, under such a design, the stress acting on the opening of the crank arm (shrink fit portion) will be too large and may exceed the yield point of the crankshaft material. In order to solve this problem, it is conceivable to reduce the stress acting on the crank arm by increasing the plate thickness of the crank arm in the central axis direction or by increasing the thickness around the opening in the radial direction.

[0011] However, when the plate thickness in the central axis direction is increased, the overall length of the crankshaft becomes longer. In this case, since the overall length of the engine also becomes longer, the internal combustion engine room becomes larger. The larger internal combustion engine room compresses the loading space for cargo, etc., which is particularly disadvantageous for marine engines.

[0012] On the other hand, when the thickness around the opening is increased in the radial direction, other components of the engine, such as the connecting rod, may come into contact with the crank arm. In order to suppress such contact, the engine needs to be designed to be higher, which still results in an increase in the size of the internal combustion engine chamber. As mentioned above, the increase in the size of the internal combustion engine chamber is particularly disadvantageous for marine engines.

[0013] In addition, if the crank arm is greatly deformed during torque transmission, the crankshaft journal will come into contact with the main bearing at one end, which may damage the main bearing. Therefore, it is necessary to find a way to increase the rigidity of the crank arm and reduce the deformation of the crank arm.

[0014] The present disclosure is made to solve the above-mentioned technical problems, and its purpose is to achieve good torque transmission and suppress damage to the main bearing without causing the internal combustion engine chamber to be enlarged.

[0015] -Technical solutions for solving technical problems-

[0016] A first aspect of the present disclosure relates to a crankshaft, which is formed by combining at least the crankshaft journal and the crank arm among a crankshaft journal, a crank pin and a crank arm by shrink fitting.

[0017] According to the first aspect of the present disclosure, the crank arm has a circular opening portion for inserting the crankshaft journal. When the crank arm is observed along the central axis of the opening portion, the direction connecting the central axis of the crank pin and the central axis of the opening portion is set as a first direction, and the direction orthogonal to the first direction is set as a second direction. The difference between the dimension from the central axis of the opening portion to the outer surface of the crank arm and the inner radius of the opening portion is taken as the thickness around the opening portion. Among the thickness around the opening portion, the thickness in the second direction will be greater than the thickness of the portion on the opposite side of the crank pin sandwiching the opening portion in the first direction.

[0018] According to the first aspect, when the thickness of the portion of the peripheral thickness in the first direction that is located on the opposite side of the crank pin with the opening clamped therein is referred to as the "first thickness", and the thickness in the second direction is referred to as the "second thickness", the first thickness will be smaller than the second thickness. The first thickness is equivalent to the thickness of the portion close to the connecting rod when the crank pin is at the bottom dead center. Therefore, by reducing the first thickness within a range where the stress acting on the shrink fit portion of the crank arm is not excessive, the crank arm can be prevented from contacting the various components constituting the engine, especially the connecting rod. As a result, the engine can be designed to be lower, thereby preventing the internal combustion engine chamber from becoming larger.

[0019] On the other hand, by making the second thickness larger than the first thickness, the rigidity of the crank arm can be increased and the deformation of the crank arm can be suppressed. The second thickness is not the plate thickness of the crankshaft in the direction of the center axis, but the thickness in the direction orthogonal to the center axis. Therefore, by relatively increasing the second thickness, the enlargement of the engine and even the internal combustion engine chamber can be suppressed, and the rigidity of the crank arm can be improved. By increasing the rigidity of the crank arm, the deformation of the crank arm during torque transmission can be suppressed, thereby avoiding one-end contact between the crankshaft journal and the main bearing. In this way, damage to the main bearing can be suppressed.

[0020] As described above, according to the first aspect, good torque transmission can be achieved and damage to the main bearing can be suppressed without increasing the size of the engine chamber.

[0021] It can also be like this, according to the second aspect of the present disclosure, when the outer surface of the crank arm that is closer to the opening portion than the crank pin in the first direction is called a first outer wall surface, at least a portion of the first outer wall surface is formed into an arc shape, and the center axis of the opening portion is offset along the first direction away from the crank pin relative to the center axis of the first outer wall surface.

[0022] According to the second aspect, as long as the central axis of the opening is offset in the first direction, the first thickness and the second thickness can be made different even without modifying the curved surface shape of the first outer wall surface. This can suppress an increase in manufacturing cost.

[0023] It may also be the case that, according to the third aspect of the present disclosure, when the inner radius of the opening is set to R, and the thickness of the portion of the thickness around the opening on the opposite side of the crank pin sandwiching the opening in the first direction is set to T1,

[0024] The relationship T1<R is satisfied.

[0025] The inventors of the present application have found through in-depth research that by designing a crank arm that satisfies the above relationship, at least the inner radius of the opening and even the shrink fit margin between the crank arm and the crankshaft journal can be ensured. As a result, better torque transmission can be achieved and damage to the main bearing can be suppressed.

[0026] It may also be the case that, according to the fourth aspect of the present disclosure, when the thickness in the second direction of the thickness around the opening is set to T2,

[0027] The relationship R<T2 is satisfied.

[0028] The inventors of the present application have conducted intensive research and found that by designing a crank arm that satisfies the above relationship, the rigidity of the crank arm can be sufficiently ensured, thereby achieving better torque transmission and suppressing damage to the main bearing.

[0029] The fifth aspect of the present disclosure relates to a marine engine, which is constructed as a two-stroke cycle internal combustion engine, comprising: a crankshaft involved in any one of the first to fourth aspects above, a bearing supporting the upper half of the crankshaft journal so that the upper half can rotate, a connecting rod connected to the crank pin, and a frame arranged on a base that accommodates the bearing and accommodates the connecting rod.

[0030] It can also be like this, according to the fifth aspect of the present disclosure, the marine engine includes a partition wall arranged in the direction of the central axis of the crankshaft and dividing the space in the frame, when the piston of the marine engine is in a state closer to the bottom dead center than the top dead center, the bearing is installed and disassembled through the space between the upper half of the crankshaft journal and the lower end of the partition wall.

[0031] According to the fifth aspect, when the crank pin is closer to the bottom dead center than the top dead center, the crank arm is in a posture with the portion corresponding to the first thickness facing upward or obliquely upward. Therefore, by making the first thickness relatively small, when the bearing is to be installed or removed through the space between the upper half of the crankshaft journal and the lower end of the partition wall, it is possible to suppress the bearing and the crank arm from contacting each other.

[0032] - Effects of the Invention -

[0033] As described above, according to the present disclosure, good torque transmission can be achieved and damage to the main bearing can be suppressed without increasing the size of the internal combustion engine chamber. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic diagram illustrating the structure of a marine engine;

[0035] Figure 2 is a side view illustrating the structure of a crankshaft;

[0036] Figure 3 is a front view illustrating the structure of a crank arm;

[0037] Figure 4 is a side view illustrating the structure of a crank arm;

[0038] Figure 5 A conventional example of a crank arm is shown. Figure 3 The corresponding figure;

[0039] Figure 6 This is a diagram illustrating the procedure for removing a bearing.

[0040] - Explanation of symbols -

[0041] 1-marine engine; 11-engine base; 12-frame; 24-connecting rod; 26-bearing; 27-partition wall; 5-crankshaft; 51-crankshaft journal; 52-crank pin; 53-crank arm; 53a-opening; 53b-outer surface of crank arm; 53c-first outer wall; A1-central axis of crankshaft journal; A2-central axis of crank pin; A3-central axis of opening; A4-central axis of first outer wall; R-inner radius of opening; T1-first thickness; T2-second thickness. DETAILED DESCRIPTION

[0042] The following is an explanation of the embodiments of the present disclosure according to the accompanying drawings. It should be noted that the following description is only an example. Figure 1 It is a schematic diagram illustrating the structure of a marine engine (hereinafter also simply referred to as “engine 1 ”).

[0043] The engine 1 is an in-line multi-cylinder diesel engine including a plurality of cylinders 16. The engine 1 is configured as a two-stroke cycle internal combustion engine of a uniflow scavenging system and is mounted on large ships such as tankers, container ships, and car carriers.

[0044] The engine 1 installed on the ship is the main internal combustion engine for moving the ship forward. To this end, the output shaft of the engine 1 is connected to the propeller (not shown) of the ship through a propeller shaft (not shown). When the engine 1 is running, the output of the engine 1 is transmitted to the propeller, allowing the ship to move forward.

[0045] In particular, in order to achieve a longer stroke of the engine 1 of the present disclosure, the engine 1 of the present disclosure is configured as a so-called crosshead internal combustion engine. That is, in the engine 1, the piston rod 22 supporting the piston 21 from below and the connecting rod 24 connected to the crankshaft 5 are connected through a crosshead 25.

[0046] (1) Main components

[0047] Next, main parts of the engine 1 will be described.

[0048] like Figure 1 As shown, the engine 1 includes a base 11 located below, a frame 12 disposed on the base 11, and a cylinder water jacket 13 disposed on the frame 12. The engine 1 also includes a cylinder 16 disposed in the cylinder water jacket 13, a piston 21 disposed in the cylinder 16, and an output shaft (a crankshaft 5 described later) that rotates in conjunction with the reciprocating movement of the piston 21.

[0049] The base 11 constitutes a crankcase of the engine 1 and houses the crankshaft 5 and a bearing 26 that rotatably supports a crank journal 51 of the crankshaft 5. The lower end of the connecting rod 24 is connected to the crankshaft 5 via a crank arm 53 and a crank pin 52.

[0050] The frame 12 contains a pair of guide plates 28, a connecting rod 24, and a crosshead 25. The pair of guide plates 28 is composed of a pair of plate-like members arranged along the axial direction of the piston 21, and is arranged in the width direction ( Figure 1 The connecting rod 24 is arranged between a pair of guide plates 28 with its lower end connected to the crankshaft 5. The upper end 24a of the connecting rod 24 is connected to the lower end of the piston rod 22 via a cross head 25.

[0051] Specifically, the crosshead 25 is arranged between a pair of guide plates 28 and slides in the up-down direction along each guide plate 28. That is, the pair of guide plates 28 is configured to guide the sliding of the crosshead 25. The crosshead 25 is connected to the piston rod 22 and the connecting rod 24 via a crosshead pin 29. The crosshead pin 29 is connected to the piston rod 22 so as to move up and down integrally, and on the other hand, the crosshead pin 29 is connected to the connecting rod 24 so as to allow the connecting rod 24 to rotate with the upper end 24a of the connecting rod 24 as a fulcrum.

[0052] The frame 12 includes a plurality of partition walls 27 for partitioning the space within the frame 12. The plurality of partition walls 27 are arranged along the central axis direction of the crankshaft 5 (in the same direction as the central axis direction of the crankshaft 5). Figure 1 Each partition wall 27 is formed into a plate shape extending perpendicularly to the central axis direction of the crankshaft 5. The partition wall 27 is arranged in the width direction of the internal combustion engine ( Figure 1 The two ends of the partition wall 27 (in the left-right direction of the paper) are respectively welded to the guide plate 28. A cutout 27a is provided at the lower end of the partition wall 27. The lower end of the partition wall 27 is opposed to the crankshaft 5, especially to the upper half of the crankshaft journal 51, with a gap in the vertical direction.

[0053] The cylinder water jacket 13 supports the cylinder liner 14 as an inner cylinder. The piston 21 is arranged inside the cylinder liner 14. The piston 21 reciprocates in the up-down direction along the inner wall of the cylinder liner 14. The cylinder head 15 and the cylinder liner 14 together constitute a cylinder 16.

[0054] An exhaust valve 18 driven by a valve driving mechanism (not shown) is provided on the cylinder head 15. The exhaust valve 18, together with the cylinder 16 formed by the cylinder liner 14 and the cylinder head 15 and the top surface of the piston 21, defines a combustion chamber 17. The exhaust valve 18 connects the combustion chamber 17 with the exhaust pipe 19 or cuts off the connection between the combustion chamber 17 and the exhaust pipe 19. The exhaust pipe 19 has an exhaust port connected to the combustion chamber 17, and the exhaust valve 18 is configured to open and close the exhaust port.

[0055] The cylinder head 15 is provided with a fuel injection valve 31 for supplying fuel to the combustion chamber 17. The fuel injection valve 31 injects diesel fuel into the combustion chamber 17.

[0056] The engine 1 according to the present embodiment includes a fuel pump 32 for delivering diesel fuel to a fuel injection valve 31 by pressure. Figure 1 As shown, the fuel pump 32 is arranged near the cylinder 16 and is fluidically connected to the fuel injection valve 31 via a fuel injection pipe (not shown).

[0057] When the engine 1 is running, diesel fuel is supplied from the fuel injection valve 31 to the combustion chamber 17, and combustion gas is supplied to the combustion chamber 17 through the cylinder water jacket 13, etc. Thus, the diesel fuel is burned in the combustion chamber 17 by the combustion gas.

[0058] Then, the piston 21 uses the energy generated by the combustion of the diesel fuel to reciprocate in the vertical direction along the cylinder liner 14. At this time, when the exhaust valve 18 operates to open the combustion chamber 17, the exhaust gas generated by the combustion is squeezed into the exhaust pipe 19. In addition, as the piston 21 reciprocates along the cylinder liner 14, the combustion gas is sucked into the cylinder liner 14 from the cylinder water jacket 13, and then the piston 21 presses the combustion gas into the combustion chamber 17, thereby redirecting the combustion gas to the combustion chamber 17. By repeating such strokes, the diesel fuel is repeatedly burned and the scavenging in the cylinder 16 is repeatedly performed.

[0059] When the piston 21 reciprocates due to combustion, the piston rod 22 reciprocates in the up-down direction together with the piston 21. In this way, the crosshead 25 connected to the piston rod 22 reciprocates in the up-down direction. The crosshead 25 allows the connecting rod 24 to rotate, and allows the connecting rod 24 to work with the connection part between it and the crosshead 25 as a fulcrum. As the connecting rod 24 works, the crank arm 53 rotates with the crank pin 52, and the crankshaft 5 rotates with the rotation. In this way, the crankshaft 5 converts the reciprocating movement of the piston 21 into a rotational motion, causing the propeller of the ship to rotate together with the propeller shaft. The ship moves forward in this way.

[0060] As described above, the torque for rotating the propeller is transmitted via the crankshaft 5. The quality of the torque transmission depends on the shape of the crankshaft 5. The shape of the crankshaft 5 may increase the size of the internal combustion engine room in which the engine 1 is mounted.

[0061] The inventors of the present application have devised a structure for the crankshaft 5 to achieve good torque transmission without increasing the size of the internal combustion engine chamber.

[0062] Next, the structure of the crankshaft 5 will be described in detail.

[0063] (2) Crankshaft structure

[0064] Figure 2 1 is a side view illustrating the structure of the crankshaft 5 . Figure 3 is a front view illustrating the structure of the crank arm 53, Figure 4 is its side view. It should be noted that Figure 3 This corresponds to the state when the crank pin 52 is at the top dead center, that is, the state when the piston 21 is at the top dead center. Figure 4 This corresponds to the state when the piston 21 is at the bottom dead center.

[0065] like Figure 2 As shown, the crankshaft 5 has a plurality of crank journals 51, a plurality of crank pins 52, and a plurality of crank arms 53 as main components. These components are repeatedly arranged in the order of crank journals 51, crank arms 53, crank pins 52, and crank arms 53 along the central axis (rotation axis A1) of the crankshaft 5.

[0066] The crankshaft 5 is formed by combining at least the crankshaft journal 51 and the crank arm 53 among the crankshaft journal 51, the crank pin 52 and the crank arm 53 by shrink fit. In other words, the crankshaft 5 is constructed as a semi-assembled or fully assembled crankshaft.

[0067] Among them, the semi-assembled crankshaft refers to a crankshaft in which the crank pin and the crank arm are manufactured as an integral component and the crankshaft journal is installed on the component by shrink fitting.

[0068] On the other hand, a fully assembled crankshaft refers to a crankshaft in which the crankshaft journal, crank pin and crank arm are manufactured as independent components and the components are combined by shrink fitting.

[0069] in particular, Figure 2 The crankshaft 5 shown is a semi-assembled crankshaft formed by combining an integral steel part consisting of a crank pin 52 and a crank arm 53 with a crank journal 51 by shrink fitting. Figure 2 The symbol Rs.

[0070] The crankshaft journal 51 is formed into a cylindrical shape. The crankshaft journal 51 has a rotation axis A1 coaxial with the propeller shaft. Figure 2 As shown, the end portion of the crank journal 51 in the direction of the rotation axis A1 is inserted into the opening 53 a of the crank arm 53 and is shrink-fitted.

[0071] Figure 1 The bearing 26 shown is a metal component constituting a main bearing (so-called "main bearing"), and supports the upper half of the crankshaft journal 51 (particularly the upper half of the non-shrink fit portion of the crankshaft journal 51) so that the upper half can rotate. By supporting the crankshaft journal 51 with the bearing 26, the crankshaft 5 can rotate about the rotation axis A1 of the crankshaft journal 51.

[0072] The crank pin 52 is formed in a cylindrical shape similar to the crank journal 51. The crank pin 52 has a central axis A2 extending parallel to the rotation axis A1 of the crank journal 51 and offset relative to the rotation axis A1. The connecting rod 24 is connected to the crank pin 52. The crank pin 52 receives power from the connecting rod 24 to rotate the entire crankshaft 5.

[0073] The crank arm 53 is formed in a plate shape orthogonal to the rotation axis A1. The crank arm 53 has a circular opening 53a into which the crank journal 51 is inserted. The central axis A3 of the opening 53a coincides with the rotation axis A1 of the crank journal 51. The crank arm 53 connects the crank journal 51 and the crank pin 52, and together with the crank journal 51 and the crank pin 52, constitutes a crank mechanism.

[0074] Next, when the crank arm 53 is observed along the central axis A3 of the opening 53a, in other words, Figure 3 As shown, when the crank arm 53 is viewed from the front, the direction connecting the central axis A2 of the crank pin 52 and the central axis A3 of the opening 53a is set as the first direction, and the direction orthogonal to the first direction is set as the second direction. Figure 4 As shown in FIG. 1 , when the crank arm 53 is viewed from the side, a direction extending along the central axis A3 of the opening 53 a is defined as a third direction.

[0075] Specifically, the first direction is equivalent to Figure 3 The second direction is equivalent to Figure 3 The third direction is equivalent to the left and right direction of the paper. Figure 3 In the following, the direction from the central axis A2 of the crank pin 52 toward the central axis A3 of the opening 53a in the first direction is referred to as "downward", and the opposite direction is referred to as "upward".

[0076] like Figure 3 As shown, the crank arm 53 faces the radial outer side of the crankshaft 5 (in other words, along the Figure 3The outer surface 53b (in the direction away from the rotation axis A1 of the paper plane) is formed so that the dimension in the first direction is longer than the dimension in the second direction.

[0077] The outer surface of the crank arm 53 at a portion closer to the opening 53a than the crank pin 52 in the first direction is referred to as a first outer wall surface 53c, and at least a portion of the first outer wall surface 53c is formed in an arc shape bulging downward.

[0078] In the present embodiment, the first outer wall surface 53c corresponds to the outer surface from the portion located at the same height as the central axis A3 of the opening 53a to the portion located below the outer surface 53b of the crank arm 53. The first outer wall surface 53c according to the present embodiment is formed in an arc shape as a whole.

[0079] like Figure 3 As shown, the central axis A3 of the opening 53a is offset in the first direction away from the crank pin 52 (downward) relative to the central axis A4 of the first outer wall surface 53c.

[0080] When the crank arm 53 is observed along the central axis A3 of the opening 53a, the difference between the dimension from the central axis A3 of the opening 53a to the outer surface 53b of the crank arm 53 and the inner radius of the opening 53a is defined as the thickness around the opening 53a. The thickness around the opening 53a in the second direction is greater than the thickness of a portion located on the opposite side of the crank pin 52 sandwiching the opening 53a in the first direction (in other words, a portion located below the opening 53a in the first direction, particularly directly below the central axis A3 of the opening 53a). Hereinafter, the latter thickness (thickness related to the first direction) is referred to as the "first thickness", and the former thickness (thickness related to the second direction) is referred to as the "second thickness".

[0081] Specifically, when the first thickness is set to T1 and the second thickness is set to T2, the following relationship is satisfied:

[0082] T1<T2 ……(1)

[0083] In other words, the first thickness T1 is equivalent to the width of the first outer wall surface 53 c when viewed along the first direction; and the second thickness T2 is equivalent to the width of the first outer wall surface 53 c when viewed along the second direction.

[0084] On the other hand, Figure 3As shown, in the case of the crank arm 53 involved in this embodiment, the central axis A3 of the opening 53a is offset downward relative to the central axis A4 of the first outer wall surface 53c. With such a structure, the second thickness T2 is kept substantially constant, and the first thickness T1 is reduced, thereby satisfying the above-mentioned relationship (1). It should be noted that the offset of the central axis A3 of the opening 53a is equal to the difference obtained by subtracting the second thickness T2 from the first thickness T1.

[0085] When the inner radius of the opening 53a is set to R, the following relationship is satisfied:

[0086] T1<R ……(2)

[0087] R<T2 ……(3)

[0088] That is, the first thickness T1 is smaller than the inner radius R of the opening 53 a . In contrast, the second thickness T2 is larger than the inner radius R of the opening 53 a .

[0089] like Figure 4 As shown, the side surface facing the crank journal 51 in the third direction is referred to as a surface 53d, and the side surface facing the crank pin 52 in the third direction is referred to as a back surface 53e. A notch 53f is provided on the back surface 53e.

[0090] Specifically, the cutout 53f according to the present embodiment is disposed below the opening 53a and is formed to the lower end of the back surface 53e. The cutout 53f is an inclined surface that is inclined from the back surface 53e side toward the front surface 53d in the third direction while heading downward in the first direction.

[0091] like Figure 4 As shown by the dot-dash line, when the crank pin 52 is at the bottom dead center, that is, when the piston 21 is at the bottom dead center, the notch 53f provided on the crank arm 53 faces the upper end portion 24a of the connecting rod 24 with a gap therebetween. By providing the notch 53f, a longer gap can be ensured between the upper end portion 24a, thereby preventing the crank arm 53 and the connecting rod 24 from contacting each other.

[0092] (3) Loading and unloading of bearings

[0093] Figure 6 This is a diagram for explaining the order of removing the bearing 26. First, return to Figure 4 , such as Figure 4 As shown, the bearing 26 is arranged in a space S between a cutout 27 a provided at a lower end portion of the partition wall 27 and an upper half portion of the crankshaft journal 51 .

[0094] like Figure 6As shown, when the piston 21 of the engine 1 is closer to the bottom dead center than the top dead center, the bearing 26 is lifted and removed by the chain pulleys 61 and 62. At this time, the bearing 26 passes directly above the portion of the crank arm 53, especially the portion corresponding to the first thickness T1.

[0095] (4) Crank arm structure

[0096] Figure 5 This is a conventional example of a crank arm 53. Figure 3 The corresponding figure. Figure 5 As shown, in the case of the crank arm 53' in the prior art, the central axis A3' of the opening 53a' to be inserted into the crank journal is coaxial with the central axis A4' of the first outer wall surface 53c' formed in a circular arc shape. In such a structure, the thickness around the opening 53a' is substantially constant. That is, when the thickness around the opening 53a' is defined as T1', which is the same as the first thickness T1, and the thickness around the opening 53a' is defined as T2', the crank arm 53' in the prior art satisfies the following relationship:

[0097] T1'=T2' ……(4)

[0098] In the conventional example, in order to improve the rigidity of the crank arm 53 ′, it is conceivable that, for example, the thicknesses T1 ′ and T2 ′ are designed to be longer than in the conventional art.

[0099] However, in such a design, other components of the engine 1 such as the connecting rod 24 may come into contact with the crank arm 53'. In order to prevent such contact, the engine 1 needs to be designed to be higher, which results in an increase in the size of the internal combustion engine room. The increase in the size of the internal combustion engine room is particularly disadvantageous for the marine engine 1.

[0100] In contrast, according to the present embodiment, the dimension of the crank arm 53 in the longitudinal direction (first direction) can be shortened by making the first thickness T1 smaller than the second thickness T2 in the thickness around the opening 53a. Figure 4 As shown, the first thickness T1 corresponds to the thickness of the portion close to the connecting rod 24 when the crank pin 52 is at the bottom dead center. Therefore, by making the first thickness T1 relatively small, it is possible to suppress the crank arm 53 from contacting the various components constituting the engine 1, especially the connecting rod 24. As a result, the engine 1 can be designed to be lower, thereby suppressing the enlargement of the internal combustion engine chamber.

[0101] On the other hand, by making the second thickness T2 greater than the first thickness T1, the rigidity of the crank arm 53 can be increased, thereby suppressing deformation of the crank arm 53. The second thickness T2 is not the plate thickness of the crankshaft 5 in the center axis direction (along the direction of the rotation axis A1), but the thickness of the crankshaft 5 in the direction orthogonal to the center axis direction (specifically, the second direction). Therefore, by relatively increasing the second thickness T2, it is possible to suppress the enlargement of the engine 1 and even the internal combustion engine chamber, and to improve the rigidity of the crank arm 53. By increasing the rigidity of the crank arm 53, it is possible to suppress deformation of the crank arm 53 during torque transmission, thereby avoiding one-end contact between the crankshaft journal 51 and the main bearing 26. In this way, damage to the bearing 26 can be suppressed.

[0102] As described above, according to the present embodiment, good torque transmission can be achieved and damage to the bearing 26 can be suppressed without increasing the size of the engine chamber.

[0103] like Figure 3 As shown, even without making any effort on the curved surface shape of the first outer wall surface 53c, the first thickness T1 and the second thickness T2 can be made different. In this way, an increase in manufacturing cost can be suppressed.

[0104] The inventors of the present application have found through intensive research that by designing the crank arm 53 to satisfy the above relationship (2), at least the inner radius R of the opening 53a and the shrink fit margin Rs between the crank arm 53 and the crank journal 51 can be ensured. As a result, better torque transmission can be achieved.

[0105] The inventors of the present application have conducted further research and found that by designing the crank arm 53 to satisfy the above relationship (3), it is possible to sufficiently ensure the rigidity of the crank arm 53. As a result, better torque transmission can be achieved.

[0106] like Figure 4 and Figure 6 As shown in FIG. 1 , when the crank pin 52 is closer to the bottom dead center than the top dead center, the crank arm 53 is in a posture in which the portion corresponding to the first thickness T1 is directed upward or obliquely upward. Therefore, by making the first thickness T1 relatively small, when the bearing 26 is to be installed or removed through the space S between the upper half of the crank journal 51 and the lower end of the partition wall 27, it is possible to suppress the bearing 26 and the crank arm 53 from contacting each other.

Claims

1. A crankshaft, wherein at least the crankshaft journal and the crank arm are combined by shrink fit, wherein: The crank arm has a circular opening for inserting the crankshaft journal. The central axis of the opening is consistent with the central axis of the crankshaft journal. When observing the crank arm along the central axis of the opening, the direction connecting the central axis of the crank pin and the central axis of the opening is set as a first direction, the direction orthogonal to the first direction is set as a second direction, and the difference between the dimension from the central axis of the opening to the outer surface of the crank arm and the inner radius of the opening is taken as the thickness around the opening. The thickness around the opening in the second direction is greater than the thickness of a portion located on the opposite side of the crank pin across the opening in the first direction.

2. The crankshaft according to claim 1, characterized in that: When the outer surface of the crank arm at a portion closer to the opening than the crank pin in the first direction is referred to as a first outer wall surface, at least a portion of the first outer wall surface is formed in an arc shape, The central axis of the opening is offset from the central axis of the first outer wall surface in the first direction away from the crank pin.

3. The crankshaft according to claim 1 or 2, characterized in that: When the inner radius of the opening is defined as R, and the thickness of the portion of the opening that is located on the opposite side of the crank pin across the opening in the first direction is defined as T1, The relationship T1<R is satisfied.

4. The crankshaft according to claim 3, characterized in that: When the thickness around the opening in the second direction is T2, The relationship R<T2 is satisfied.

5. A marine engine, characterized in that: The marine engine is configured as a two-stroke cycle internal combustion engine, comprising: a crankshaft as claimed in any one of claims 1 to 4, a bearing supporting an upper half of the crankshaft journal so that the upper half can rotate, a connecting rod connected to the crank pin, and a frame provided on a base accommodating the bearing and accommodating the connecting rod, The marine engine includes partition walls arranged in a direction of the central axis of the crankshaft and partitioning a space in the frame. When the piston of the marine engine is in a state closer to the bottom dead center than the top dead center, the bearing is installed or removed through a space between the upper half of the crankshaft journal and the lower end of the partition wall.

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